Surface preparation prior to deposition

ABSTRACT

Methods are provided herein for treating substrate surfaces in preparation for subsequent nucleation-sensitive depositions (e.g., polysilicon or poly-SiGe) and adsorption-driven deposition (e.g. atomic layer deposition or ALD). Prior to depositing, the surface is treated with non-depositing plasma products. The treated surface more readily nucleates polysilicon and poly-SiGe (such as for a gate electrode), or more readily adsorbs ALD reactants (such as for a gate dielectric). The surface treatment provides surface moieties more readily susceptible to a subsequent deposition reaction, or more readily susceptible to further surface treatment prior to deposition. By changing the surface termination of the substrate with a low temperature radical treatment, subsequent deposition is advantageously facilitated without depositing a layer of any appreciable thickness and without significantly affecting the bulk properties of the underlying material. Preferably less than 10 Å of the bulk material incorporates the excited species, which can include fluorine, chlorine and particularly nitrogen excited species.

REFERENCE TO PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/626,212 (filed 24 Jul. 2003), which is a continuation of U.S. patentapplication Ser. No. 09/944,734 (filed 31 Aug. 2001; issued as U.S. Pat.No. 6,613,695), which claims the benefit of U.S. Provisional PatentApplication 60/253,693 (filed 24 Nov. 2000) and U.S. Provisional PatentApplication 60/283,584 (filed 13 Apr. 2001). The entire disclosure ofall of these priority applications is hereby incorporated by referenceherein.

FIELD OF THE INVENTION

The invention relates generally to surface preparation prior to filmdeposition for semiconductor fabrication, and are particularly tosurface preparation to facilitate adsorption in subsequent atomic layerdeposition (ALD) processes, or to facilitate nucleation of subsequentchemical vapor deposition processes.

BACKGROUND OF THE INVENTION

Integrated circuit design is constantly being scaled down in pursuit offaster circuit operation and lower power consumption. Scaled dimensionsin a circuit design generally requires attendant changes in fabricationprocessing.

A basic building block of integrated circuits is the thin filmtransistor (TFT). As is known in the art, the transistor typicallyincludes a gate electrode separated from a semiconductor layer orsubstrate by a thin gate dielectric material. Although a common acronymfor state-of-the-art transistors is MOS, for metal-oxide-silicon, thematerial of choice for the gate electrode has long been silicon ratherthan metal. Among other advantages, silicon gate electrodes are able towithstand high temperature processes and enable self-aligned dopingprocesses used for completing the transistor, thus saving expensivemasking steps.

Accordingly, conventional gate electrodes are formed of polysilicondoped with conductivity-enhancing impurities, such as arsenic,phosphorus or boron. Silicon can be deposited by CVD with in situ dopingby flowing a dopant source gas (e.g., arsine, phosphine, diborane, etc.)concurrently with a silicon source gas (e.g. silane).

Recently, interest has been drawn to the possibility of doping siliconelectrodes with germanium, thereby reducing the electrical work functionof the transistor gate electrode. Accordingly, a reduced voltage isneeded to operate the circuit, consequently generating less heat.Moreover, a silicon germanium gate electrode remains compatible withsurrounding materials and current integrated circuit fabricationprocesses. Proposals for flowing silicon germanium layers include insitu doping of a silicon layer by forming germane (GeH₄) along withsilane (SiH₄) in a chemical vapor deposition (CVD) process.

While in situ doped CVD processes have been found to be effective inproducing silicon germanium, the addition of germane to the silane flowhas been found to significantly increase incubation or nucleation timesover dielectric materials, particularly oxides such as silicon dioxideand some of the high-k materials discussed below. Similarly slownucleation over dielectric materials occurs when chemical vapordepositing polysilicon, and is particularly acute when in situ flowingother dopant source gases.

Slow nucleation entails higher overall deposition times, lowerthroughput and consequently greater fabrication costs. The semiconductorindustry is very sensitive to fabrication costs. Accordingly, anyincrease in wafer throughput, at any stage of processing, translates toreduced production costs and higher margins. Furthermore, the initialpoor nucleation can lead to poor quality of the resultant layer,including problems with stoichiometry, density, surface planarity, etc.

One way in which SiGe or other in situ doped silicon deposition has beenhastened is by the first formation of a nucleation layer, typically ofpolysilicon, over the gate dielectric, followed by poly-SiGe deposition.However, this additional step complicates the process flow and requiresadjustment of the doping concentrations at the dielectric-electrodeinterface to ensure the desired work function for the transistor.

Another area in which process control is particularly critical is thefabrication of transistor gate dielectrics. In the pursuit of everfaster and more efficient circuits, semiconductor designs arecontinually scaled down with each product generation. Transistorswitching time plays a large role in the pursuit of faster circuitoperation. Switching time, in turn, can be reduced by reducing thechannel length of the transistors. In order to realize maximumimprovements in transistor performance, vertical dimensions should bescaled along with horizontal dimensions. Accordingly, effective gatedielectric thickness, junction depth, etc. will all decrease with futuregeneration integrated circuits.

Conventional gate dielectrics are formed of high quality silicon dioxideand are typically referred to as “gate oxide” layers. Ultra thin gateoxides (e.g., less than 5 nm), however, have been found to exhibit highdefect densities, including pinholes, charge trapping states, andsusceptibility to hot carrier injection effects. Such high defectdensities lead to leakage currents through the gate dielectric and rapiddevice breakdown unacceptable for circuit designs with less than 0.25 μmgate spacing, i.e., sub-quarter-micron technology.

While care under laboratory conditions can be used to control defectdensities, such control has been difficult to achieve under commercialvolume fabrication conditions. Moreover, even if the integrity of theoxide is perfectly maintained, quantum-mechanical effects setfundamental limits on the scaling of gate oxide. At high fields, directtunneling dominates over Fowler-Nordheim tunneling, and largelydetermines oxide scaling limits. These scaling limits have beenestimated at about 2 nm for logic circuits, and about 3 nm for moreleakage-sensitive memory arrays in dynamic random access memory (DRAM)circuits. See, e.g., Hu et al., “Thin Gate Oxides Promise HighReliability,” SEMICONDUCTOR INTERNATIONAL (July 1998), pp. 215-222.

Theoretically, incorporating materials of higher dielectric constantinto the gate dielectric opens the door to further device scaling. Dueto higher dielectric constant, many materials can exhibit the samecapacitance as a thinner silicon dioxide layer, such that a lowerequivalent oxide thickness can be achieved without tunnel-limitedbehavior. Silicon nitride (Si₃N₄), for example, has a higher dielectricconstant than SiO₂ and also demonstrates good diffusion barrierproperties, resisting boron penetration. More exotic materials with evenhigher dielectric constants, including aluminum oxide (Al₂O₃), zirconiumoxide (ZrO₂), hafnium oxide (HfO₂), barium strontium titanate (BST),strontium bismuth tantalate (SBT), tantalum oxide (Ta₂O₅), etc., arealso being investigated to allow further device scaling.

Similar high quality, thin dielectric layers are desirable in othercontexts of integrated circuit fabrication. Integrated capacitors inmemory arrays must exhibit a certain minimum capacitance for proper datastorage and retrieval. Some efforts to increase capacitance for a givenmemory cell space have focused on the use of materials characterized byhigh dielectric constants (high k materials), such as those listedabove.

As noted above, it is often difficult to deposit electrode materials,such as polysilicon, amorphous silicon, and particularly doped siliconor silicon germanium alloys, over conventional silicon oxides as well asmany of the high k materials currently under investigation. Many othertypes of materials and deposition techniques in integrated circuitfabrication face issues that depend upon the substrate surface uponwhich the material is to be deposited.

Intermediate layers are often deposited prior to deposition of thedesired functional layer for a variety of remedial reasons, includingotherwise poor adhesion, nucleation, electrical interface properties,diffusion, etc. Such intermediate layers add to the complexity and costof fabrication, and can also occupy valuable space within high aspectratio features, such as contact vias or folded structures for highsurface area capacitors. In some contexts, like gate dielectrics andcapacitor dielectrics, additional layers increase the overall dielectricthickness and reduce the effectiveness of the layer, contrary to thetrend for scaling down integrated circuits.

Accordingly, a need exists for improving the speed, efficiency, qualityand uniformity of depositing layers in semiconductor fabrication.

SUMMARY OF THE INVENTION

In satisfaction of this need, methods are provided herein for treatingsubstrate surfaces in preparation for subsequent deposition. Inparticular, the methods are provided for preceding nucleation sensitivedepositions (e.g., polysilicon or poly-SiGe) and adsorption drivendeposition (e.g. atomic layer deposition or ALD).

Prior to depositing, the preferred embodiments treat the surface withplasma products. Advantageously, CVD polysilicon and poly-SiGe morereadily nucleates over the treated surface, or ALD reactants morereadily adsorb upon the treated surface. The surface treatment providessurface moieties more readily susceptible to a subsequent depositionreaction, or more readily susceptible to further surface treatment priorto deposition. By changing the surface termination of the substrate witha low temperature radical treatment, subsequent deposition isadvantageously facilitated without depositing a layer of any appreciablethickness and without significantly affecting the bulk properties of theunderlying material.

Exemplary plasma product treatment includes provision of F, Cl, H or Nradicals, particularly through a remote plasma module attached to adeposition chamber for in situ surface treatment prior to deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be readily apparent fromthe following description and from the appended drawings, which aremeant to illustrate and not to limit the invention, and wherein:

FIG. 1 is a schematic sectional view of an exemplary single-substratereaction chamber;

FIG. 2 is a gas flow schematic, illustrating reactant and purge gassources in accordance with a preferred embodiment of the presentinvention;

FIG. 3 is a flow chart generally showing steps for treating substratesin accordance with the preferred embodiments;

FIGS. 4A and 4B are schematic sections of a transistor gate stackconstructed in accordance with preferred embodiments of the invention;and

FIG. 5 is a flow chart illustrating the sequence for two embodiments ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The skilled artisan will readily appreciate that the principlesdisclosed herein will have application to a variety of contexts in whichinterface preparation prior to deposition is desired. Such preparationis particularly advantageous for nucleation-sensitive andadsorption-driven processes.

In accordance with the preferred embodiments, the invention providestreatment of surfaces with plasma products prior to deposition. Theplasma products preferably modify surface termination to make themsusceptible to subsequent deposition

As noted in the Background section above, many deposition processes aresensitive to the surface over which deposition is required. Dopedpolysilicon and polycrystalline silicon-germanium alloy (poly-SiGe) tendto nucleate poorly over silicon oxide, as is well known in the art, andalso over newer high-k materials now being investigated. The presentinvention provides a method for preparing the dielectric surface forelectrode deposition thereover, advantageously without significantdeposition and preferably without significant modification of bulkproperties of the dielectric.

Another deposition technique facilitated by the methods of the preferredembodiments is atomic layer deposition (ALD). ALD is a self-limitingprocess, whereby alternated pulses of reaction precursors saturate asubstrate and leave no more than one monolayer of material per pulse.The precursors are selected to ensure self-saturating reactions, becausean adsorbed layer in one pulse leaves a surface termination that isnon-reactive with the gas phase reactants of the same pulse. Asubsequent pulse of different reactants do react with the previoustermination to enable continued deposition. Thus, each cycle ofalternated pulses leaves no more than about one molecular layer of thedesired material. The principles of ALD type processes have beenpresented by T. Suntola, e.g. in the Handbook of Crystal Growth 3, ThinFilms and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14,Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B. V. 1994, thedisclosures of which are incorporated herein by reference.

Unfortunately, depending upon the chemistries employed, ALD does notdeposit equally well on different starting substrates. Some ALD processrecipes, for example, have been found slow or even non-operative indepositing over silicon, and particularly etched or cleaned siliconsurfaces (typically hydrogen-terminated). For example, it is unlikelythat aluminum alkyls, such as (CH₃)₃Al, can attach on ahydrogen-terminated silicon surface in ALD processes for depositingAl₂O₃.

However, a first water pulse may react with the silicon surface andleave a hydroxyl terminated (—OH) or oxygen bridged (Si—O—Si) siliconsurface that serves as a starting surface for the chemisorption ofaluminum alkyls. The ALD process can proceed thereafter, as thepreferred precursors readily react with SiO₂ to deposit Al₂O₃ thereover.

Prior to describing the processes in greater detail, the preferredreactor for depositing polysilicon and poly-SiGe by CVD is firstdescribed below. While not illustrated separately, the ALD processesdescribed below are more preferably performed in a Pulsar™ 2000 ALCVD™Reactor, commercially available from ASM Microchemistry Oy of Espoo,Finland, which can also be modified to have a remote plasma processingunit connected thereto.

Preferred Reactor

While the preferred embodiments are presented in the context of asingle-substrate, horizontal flow cold-wall reactor, it will beunderstood that certain aspects of the invention will have applicationto reactors of other types. The illustrated single-pass horizontal flowdesign enables laminar flow of reactant gases, with low residence times,which in turn facilitates sequential processing while minimizingreactant interaction with each other and with chamber surfaces. Thus,among other advantages, such a laminar flow enables sequentially flowingreactants that might react with each other. Reactions to be avoidedinclude highly exothermic or explosive reactions, such as produced byoxygen and hydrogen-bearing reactants, and reactions that produceparticulate contamination of the chamber. The skilled artisan willrecognize, however, that for certain sequential processes, other reactordesigns can also be provided for achieving these ends, providedsufficient purge time is allowed to remove incompatible reactants.

FIG. 1 shows a chemical vapor deposition (CVD) reactor 10, including aquartz process or reaction chamber 12, constructed in accordance with apreferred embodiment, and for which the methods disclosed herein haveparticular utility. While originally designed to optimize epitaxialdeposition of silicon on a single substrate at a time, the inventorshave found the superior processing control to have utility in CVD of anumber of different materials. Moreover, the illustrated reactor 10 cansafely and cleanly accomplish multiple treatment steps sequentially inthe same chamber 12. The basic configuration of the reactor 10 isavailable commercially under the trade name Epsilon® from ASM America,Inc. of Phoenix, Ariz.

A plurality of radiant heat sources are supported outside the chamber 12to provide heat energy in the chamber 12 without appreciable absorptionby the quartz chamber 12 walls. While the preferred embodiments aredescribed in the context of a “cold wall” CVD reactor for processingsemiconductor wafers, it will be understood that the processing methodsdescribed herein will have utility in conjunction with otherheating/cooling systems, such as those employing inductive or resistiveheating.

The illustrated radiant heat sources comprise an upper heating assemblyof elongated tube-type radiant heating elements 13. The upper heatingelements 13 are preferably disposed in spaced-apart parallelrelationship and also substantially parallel with the reactant gas flowpath through the underlying reaction chamber 12. A lower heatingassembly comprises similar elongated tube-type radiant heating elements14 below the reaction chamber 12, preferably oriented transverse to theupper heating elements 13. Desirably, a portion of the radiant heat isdiffusely reflected into the chamber 12 by rough specular reflectorplates (not shown) above and below the upper and lower lamps 13, 14,respectively. Additionally, a plurality of spot lamps 15 supplyconcentrated heat to the underside of the substrate support structure(described below), to counteract a heat sink effect created by coldsupport structures extending through the bottom of the reaction chamber12.

Each of the elongated tube type heating elements 13, 14 is preferably ahigh intensity tungsten filament lamp having a transparent quartzenvelope containing a halogen gas, such as iodine. Such lamps producefull-spectrum radiant heat energy transmitted through the walls of thereaction chamber 12 without appreciable absorption. As is known in theart of semiconductor processing equipment, the power of the variouslamps 13, 14, 15 can be controlled independently or in grouped zones inresponse to temperature sensors.

A substrate, preferably comprising a silicon wafer 16, is shownsupported within the reaction chamber 12 upon a substrate supportstructure 18. Note that, while the substrate of the illustratedembodiment is a single-crystal silicon wafer, it will be understood thatthe term “substrate” broadly refers to any surface on which a layer isto be deposited. Moreover, the principles and advantages describedherein apply equally well to depositing layers over numerous other typesof substrates, including, without limitation, glass substrates such asthose employed in flat panel displays.

The illustrated support structure 18 includes a substrate holder 20,upon which the wafer 16 rests, and a support spider 22. The spider 22 ismounted to a shaft 24, which extends downwardly through a tube 26depending from the chamber lower wall. Preferably, the tube 26communicates with a source of purge or sweep gas which can flow duringprocessing, inhibiting process gases from escaping to the lower sectionof the chamber 12.

A plurality of temperature sensors are positioned in proximity to thewafer 16. The temperature sensors may take any of a variety of forms,such as optical pyrometers or thermocouples. The number and positions ofthe temperature sensors are selected to promote temperature uniformity,as will be understood in light of the description below of the preferredtemperature controller. Preferably, however, the temperature sensorsdirectly or indirectly sense the temperature of positions in proximityto the wafer.

In the illustrated embodiment, the temperature sensors comprisethermocouples, including a first or central thermocouple 28, suspendedbelow the wafer holder 20 in any suitable fashion. The illustratedcentral thermocouple 28 passes through the spider 22 in proximity to thewafer holder 20. The reactor 10 further includes a plurality ofsecondary or peripheral thermocouples, also in proximity to the wafer16, including a leading edge or front thermocouple 29, a trailing edgeor rear thermocouple 30, and one or more side thermocouples (not shown).Each of the peripheral thermocouples are housed within a slip ring 32,which surrounds the substrate holder 20 and the wafer 16. Each of thecentral and peripheral thermocouples are connected to a PID temperaturecontroller, which sets the power of the various heating elements 13, 14,15 in response to the readings of the thermocouples.

In addition to housing the peripheral thermocouples, the slip ring 32absorbs and emits radiant heat during high temperature processing, suchthat it compensates for a tendency toward greater heat loss orabsorption at wafer edges, a phenomenon which is known to occur due to agreater ratio of surface area to volume in regions near such edges. Byminimizing edge losses, the slip ring 32 can reduce the risk of radialtemperature non-uniformities across the wafer 16. The slip ring 32 canbe suspended by any suitable means. For example, the illustrated slipring 32 rests upon elbows 34 which depend from a front chamber divider36 and a rear chamber divider 38. The dividers 36, 38 desirably areformed of quartz. In some arrangements, the rear divider 38 can beomitted.

The illustrated reaction chamber 12 includes an inlet port 40 for theinjection of reactant and carrier gases, and the wafer 16 can also bereceived therethrough. An outlet port 42 is on the opposite side of thechamber 12, with the wafer support structure 18 positioned between theinlet 40 and the outlet 42.

An inlet component 50 is fitted to the reaction chamber 12, adapted tosurround the inlet port 40, and includes a horizontally elongated slot52 through which the wafer 16 can be inserted. A generally verticalinlet 54 receives gases from remote sources, as will be described morefully with respect to FIG. 2, and communicates such gases with the slot52 and the inlet port 40. The inlet 54 can include gas injectors asdescribed in U.S. Pat. No. 5,221,556, issued Hawkins et al., or asdescribed with respect to FIGS. 21-26 in U.S. Pat. No. 6,093,252, issuedJul. 25, 2000, the disclosures of which are hereby incorporated byreference. Such injectors are designed to maximize uniformity of gasflow for the single-wafer reactor.

An outlet component 56 similarly mounts to the process chamber 12 suchthat an exhaust opening 58 aligns with the outlet port 42 and leads toexhaust conduits 59. The conduits 59, in turn, can communicate withsuitable vacuum means (not shown) for drawing process gases through thechamber 12. In the preferred embodiment, process gases are drawn throughthe reaction chamber 12 and a downstream scrubber (not shown). A pump orfan is preferably included to aid in drawing process gases through thechamber 12, and to evacuate the chamber for low pressure processing.

The preferred reactor 10 also includes a source 60 of excited species,preferably positioned upstream from the chamber 10. The excited speciessource 60 of the illustrated embodiment comprises a remote plasmagenerator, including a magnetron power generator and an applicator alonga gas line 62. An exemplary remote plasma generator is availablecommercially under the trade name TRW-850 from Rapid Reactive RadicalsTechnology (R3T) GmbH of Munich, Germany. In the illustrated embodiment,microwave energy from a magnetron is coupled to a flowing gas in anapplicator along a gas line 62. A source of precursor gases 63 iscoupled to the gas line 62 for introduction into the excited speciesgenerator 60. A source of carrier gas 64 is also coupled to the gas line62. One or more further branch lines 65 can also be provided foradditional reactants. As is known in the art, the gas sources 63, 64 cancomprise gas tanks, bubblers, etc., depending upon the form andvolatility of the reactant species. Each gas line can be provided with aseparate mass flow controller (MFC) and valves, as shown, to allowselection of relative amounts of carrier and reactant species introducedto the excited species generator 60 and thence into the reaction chamber12.

It will be understood that, in other arrangements, the excited speciescan be generated within the process chamber. For example, in situplasmas can be generated by applying radio frequency (RF) power tospaced electrodes within the process chamber, as is known in the art.Exemplary in situ plasma CVD reactors are available, for example, fromASM Japan K. K. of Tokyo, Japan under the trade name Eagle™ 10 or Eagle™12. Furthermore, energy can be coupled to source gases by a number ofmeans, including by induction, capacitively, etc., for either in situ orremote plasma generation. Preferably, however, a remote plasma source isemployed for the processes described herein, affording greater controlfor surface modification with minimal bulk effects.

Wafers are preferably passed from a handling chamber (not shown), whichis isolated from the surrounding environment, through the slot 52 by apick-up device. The handling chamber and the processing chamber 12 arepreferably separated by a gate valve (not shown) of the type disclosedin U.S. Pat. No. 4,828,224, the disclosure of which is herebyincorporated herein by reference.

The total volume capacity of a single-wafer process chamber 12 designedfor processing 200 mm wafers, for example, is preferably less than about30 liters, more preferably less than about 20 liters, and mostpreferably less than about 10 liters. The illustrated chamber 12 has acapacity of about 7.5 liters. Because the illustrated chamber 12 isdivided by the dividers 32, 38, wafer holder 20, ring 32, and the purgegas flowing from the tube 26, however, the effective volume throughwhich process gases flow is around half the total volume (about 3.77liters in the illustrated embodiment). Of course, it will be understoodthat the volume of the single-wafer process chamber 12 can be different,depending upon the size of the wafers for which the chamber 12 isdesigned to accommodate. For example, a single-wafer processing chamber12 of the illustrated type, but for 300 mm wafers, preferably has acapacity of less than about 100 liters, more preferably less than about60 liters, and most preferably less than about 30 liters. One 300 mmwafer processing chamber has a total volume of about 24 liters, with aneffective processing gas capacity of about 11.83 liters.

FIG. 2 shows a gas line schematic, in accordance with the preferredembodiment. The reactor 10 is provided with a source 70 of oxidizingagent or oxidant. The oxidant source 70 can comprise any of a number ofknown oxidants, particularly a volatile oxidant such as O₂, O₃, NO, H₂O,N₂O, HCOOH, HClO₃. Preferably, the oxidant is introduced in an inertcarrier gas flow, such as N₂. In other arrangements, pure reactant flowscan also be used. In still other arrangements, an oxygen-containingsource gas can be provided to the remote plasma generator 60 to provideexcited species for oxidation.

As also shown in FIG. 2, the reactor 10 further includes a source 72 ofhydrogen gas (H₂). As is known in the art, hydrogen is a useful carriergas and purge gas because it can be provided in very high purity, due toits low boiling point, and is compatible with silicon deposition. H₂ canalso be employed in a high temperature hydrogen bake to sublimate nativeoxide prior to layer formation. H₂ can also flow through the excitedspecies generator 60 to generate H radicals for native oxide cleaning orfor other purposes.

The preferred reactor 10 also includes a source 73 of nitrogen gas (N₂).As is known in the art, N₂ is often employed in place of H₂ as a carrieror purge gas in semiconductor fabrication. Nitrogen gas is relativelyinert and compatible with many integrated materials and process flows.Other possible carrier gases include noble gases, such as helium (He) orargon (Ar).

A liquid reactant source 74 is also shown. The liquid source 74 cancomprise, for example, liquid dichlorosilane (DCS), trichlorosilane(TCS) or higher order silane sources in a bubbler, and a gas line forbubbling and carrying vapor phase reactants from the bubbler to thereaction chamber 12. The bubbler can alternatively (or additionally)hold liquid Ta(OC₂H₅)₅ as a metal source, while a gas line serves tobubble H₂, N₂, Ne, He or Ar through the liquid metal source andtransport metallorganic precurors to the reaction chamber 12 in gaseousform.

Desirably, the reactor 10 will also include other source gases such asdopant sources (e.g., the illustrated phosphine 76, arsine 78 anddiborane 80 sources) and etchants for cleaning the reactor walls andother internal components (e.g., HCl source 82 or NF₃/Cl₂ provided asthe plasma source gas 63 for feeding the excited species generator 60).For deposition of poly-SiGe in accordance with the preferredembodiments, a source of germanium 84 (e.g., germane or GeH₄) is alsoprovided for doping or formation of SiGe films.

Additional source gases include an ammonia (NH₃) source (not shown),which serves as a volatile nitrogen source, useful in CVD andnitridation anneal steps. A silicon source 86 is also provided,illustrated as monosilane (SiH₄). As is known in the art, silanes,including monosilane (SiH₄), disilane (Si₂H₆), trisilane (Si₃H₈), DCSand TCS, are volatile silicon sources for CVD applications, such as thedeposition of poly-SiGe, silicon nitride, metal silicides, and extrinsicor intrinsic silicon (polycrystalline, amorphous or epitaxial, dependingupon deposition parameters). Monosilane (SiH₄), as illustrated, isparticularly preferred to avoid chlorine incorporation into sensitivegate dielectric structures.

Each of the gas sources may be connected to the inlet 54 (FIG. 1) viagas lines with attendant safety and control valves, as well as mass flowcontrollers (“MFCs”), which are coordinated at a gas panel. Processgases are communicated to the inlet 54 (FIG. 1) in accordance withdirections programmed into a central controller and distributed into theprocess chamber 12 through injectors. After passing through the processchamber 12, unreacted process gases and gaseous reaction by-products areexhausted to a scrubber 88 to condense environmentally dangerous fumesbefore exhausting to the atmosphere.

In addition to the conventional gas sources and liquid bubblers,discussed above, the preferred reactor 10 includes the excited speciessource 60 positioned remotely or upstream of the reaction chamber 12.The illustrated source 60 couples microwave energy to gas flowing in anapplicator, where the gas includes reactant precursors from the reactantsource 63. For the processes described below, the plasma source gases 63include a source of fluorine (e.g., NF₃, F₂ or B₂F₆), a source ofchlorine (e.g., Cl₂) and/or a source of nitrogen (e.g., N₂ or NH₃).Other useful plasma source gases for the preferred processes include H₂,O₂, NO, N₂O, He, and Ar. A plasma is ignited within the applicator, andexcited species are carried toward the chamber 12. Preferably, of theexcited species generated by the source 60, overly reactive ionicspecies substantially recombine prior to entry into the chamber 12. Onthe other hand, radicals such as F, Cl, N or O survive to enter thechamber 12 and react as appropriate. As will be clear from the generalprocess discussion below, remote plasma-generated excited speciesfacilitate higher quality layers as well as possible greater waferthroughput.

Process Flow

FIG. 3 shows a general process sequence in accordance with theinvention, illustrated in the context of forming a transistor gate stackon a semiconductor substrate. As illustrated, a single substrate,including a semiconductor structure, is first cleaned 100 to removecontaminants and naturally occurring or native oxide on thesemiconductor structure. The semiconductor structure can comprise, amongother things, an epitaxial silicon layer or the top surface of amonolithic silicon layer. Conventionally, wafer cleaning prior to gateoxide growth is conducted ex situ prior to loading the wafer into theprocess chamber. For example, wafers may be cleaned in an SCl/HF wetetch bath. Alternatively, an integrated HF and acetic acid vapor cleancan be conducted in a neighboring module within a cluster tool, reducingtransport time and opportunity for recontamination or reoxidation. Forsome applications, the cleaning oxide left by the SC1 step is notremoved, but is instead used as the initial oxide layer. In anotherpossibility, a hydrogen bake step can be conducted within the chamber 12to sublimate native oxide. Small amounts of HCl vapor can be added tothis step to aid in cleaning metal contaminants and the like during thehydrogen bake. In still another arrangement, plasma products can assistor conduct in situ cleaning, such as by substituting H radicals forhydrogen gas.

Either after ex situ cleaning, or prior to in situ cleaning, the waferor other substrate is loaded into the process chamber. Cleaning 100 ofnative oxide tends to leave a hydrogen-terminated surface, whichadvantageously inhibits spontaneous reoxidation upon exposure to theclean room environment or other source of oxidants. Unfortunately, suchhydrogen termination can also inhibit subsequent ALD processes, such asthe illustrated ALD deposition of ZrO₂ or Al₂O₃. One method offacilitating adsorption of reactants is to deposit a thin interfaciallayer. Disadvantageously, however, such a layer increases the overallthickness of the dielectric to be formed upon the substrate and alsotends to decrease the effective dielectric constant.

Accordingly, the preferred embodiments employ an excited speciestreatment 110 of the cleaned substrate surface, preferably conducted inthe same chamber as a subsequent deposition 120 of the gate dielectric.The treatment modifies the surface termination of the substrate topromote subsequent deposition. Advantageously, the treatment 110 istuned such that the excited species impart sufficient activation energyto break the surface bonds (in the illustrated embodiment, ofhydrogen-silicon bonds and Si—Si bonds) and form new ones, whiletemperature is maintained low enough to prevent etching of the substrateor significant diffusion of active species into the bulk material.Additionally, no appreciable deposition takes place. At the most, amonolayer of terminating tails is left by the excited species treatment110. As discussed below, while no deposition beyond surface terminationtakes place, some conversion of the top few monolayers of the substratecan be advantageous.

The excited species treatment can be conducted in situ in the samechamber as a subsequent dielectric deposition 120. In this case, thesubstrate temperature is preferably set to match that desired for thesubsequent deposition 120 within the same chamber.

In one embodiment, the excited species treatment 110 includes exposureto fluorine or chlorine radicals in sufficient supply to break surfacebonds, but insufficient to etch the preferred silicon surface. Sourcesgases provided to the preferred remote plasma generator 60 (FIG. 2)include NF₃, F₂, B₂F₆, Cl₂, CF₄, etc. Argon, helium or other inert gascan also flow to aid formation of glow discharge and serve as carriergas, but the total flow rates and partial pressures are preferablyarranged to keep reaction chamber pressure below about 10 Torr formaintaining operation of the remote plasma unit. Preferably, the processparameters are tuned to be sufficient for breaking surface bonds withoutsignificant bulk modification. In the illustrated embodiments, whereinsubsequent deposition 120 is conducted in situ by ALD, temperatures arepreferably in the range of room temperature to 700° C., more preferablyfrom 200° C. to 500° C. For the given temperature, pressure, remoteplasma power, reaction times and reactant concentrations are adjusted toachieve the desired surface conditioning.

In another embodiment, a nitrogen source, such as ammonia (NH₃) ornitrogen gas (N₂) can be supplied to the substrate to break surfacebonds and create Si—N bonds, depending on the nature of the subsequentdeposition. Argon, helium or other inert gas can also flow to aidformation of glow discharge and serve as carrier gas, but the total flowrates are partial pressures are preferably arranged to keep reactionchamber pressure below about 10 Torr for maintaining operation of theremote plasma unit. As noted, the process does not result in a depositedlayer. Process parameters are preferably selected to replace Si—Si bondsin the upper few monolayers of the substrate with Si—N bonds,particularly converting less than about 10 Å of the substrate surface tosilicon oxynitride, more preferably forming about 2 Å to 5 Å on average.Process parameters are set to avoid significant nitrogen diffusion intothe bulk, beyond the nitrogen incorporation in the upper few monolayersof the substrate. Preferably, the bulk substrate contains less thanabout 1% atomic concentration of nitrogen. As noted with respect to F orCl treatment, the excited species treatment 110 can be conducted in situwith subsequent high k dielectric formation 120, such that the sametemperature range as the subsequent deposition can be employed for theexcited species treatment 110. For the given temperature, pressure,remote plasma power, process duration and reactant concentrations can beadjusted to for the desired limitations on nitrogen penetration into thebulk.

Following excited species treatment 110, the gate dielectric isdeposited 120 over the treated surface. The deposition 120 can alsoinclude radical species flow; however, in such a case, the radicalsupply from the excited species treatment 110 will typically bedifferent from the supply employed in the deposition 120. Accordingly,the flow of radicals from the excited species treatment 110 ispreferably stopped prior to deposition 120.

In accordance with the preferred embodiment, the deposition 120comprises an ALD-type deposition, wherein alternated pulses saturate thesurface, and each cycle leaves no more than about 1 monolayer of thedielectric material. In the examples below, an aluminum source gas orzirconium source gas is alternated with an oxygen source gas to formaluminum oxide (Al₂O₃) and zirconium oxide (ZrO₂). The skilled artisanwill appreciate that similar recipes can be employed other high kmaterials, such as hafnium oxide (HfO₂), tantalum oxide (Ta₂O₅), bariumstrontium titanate (BST) or strontium bismuth tantalate (SBT).

The first pulse of the ALD deposition advantageously reacts with thetermination left by the excited species surface treatment 110.Alternatively, a further surface treatment can be provided prior to thedeposition. For example, a water treatment can more readily react withthe surface after the excited species treatment 110, to leave ahydroxyl-terminated surface that readily react with subsequent ALDprocesses.

In one embodiment, either before or after the excited species treatment110, the silicon wafer was loaded into the reaction space of Pulsar™2000 reactor (commercially available from ASM Microchemistry of Espoo,Finland), which is designed for ALD processes. The reaction space wasevacuated to vacuum with a mechanical vacuum pump. After evacuation thepressure of the reaction space was adjusted to about 5-10 mbar(absolute) with flowing inert gas (e.g., helium, argon or nitrogen gas)that had a purity of 99.9999%. Then the reaction space was stabilized at300° C. Alternating vapor phase pulses of (CH₃)₃Al and H₂O, vaporizedfrom external sources, were introduced into the reaction space andcontacted with the substrate surface. The source chemical pulses wereseparated from each other with flowing nitrogen gas.

Each pulsing cycle consists of four basic steps:

(CH₃)₃Al pulse

N₂ purge

H₂O pulse

N₂ purge

An exemplary aluminum oxide deposition cycle is summarized in Table I.TABLE I Al₂O₃ Temperature Pressure Time Phase Reactant (° C.) (mbar(sec) pulse 1 TMA 300 5-10 0.2 purge 1 — 300 5-10 1.1 pulse 2 H₂O 3005-10 1.5 purge 2 — 300 5-10 3.0

The number of cycles determine the thickness of the layer. The growthrate of Al₂O₃ from (CH₃)₃Al and H₂O is typically near 0.1 nm/cycle or 1Å/cycle at 300° C., or about 3-4 cycles/monolayer (Al₂O₃ has a bulklattice parameter of about 3 Å). The methyl terminations left by eachTMA pulse reduce the number of available chemisorption sites, such thatless than a full monolayer forms with each pulse. The pulsing cycle isrepeated sufficient times to produce the desired layer thickness.Aluminum oxide can be used as the gate dielectric, or as a thin layerprior to forming another dielectric layer.

In another arrangement, ZrO₂ is deposited by an ALD type process. ZrCl₄vapor is introduced to the reaction chamber and exposed the wafersurface for 1.5 s. This is referred to as pulse A. The reaction chamberwas purged with nitrogen gas for 3.0 s to remove surplus ZrCl₄ andbyproducts from the reaction chamber. This is referred to as purge A.Then water vapor was introduced to the reaction chamber and exposed tothe wafer surface for 3.0 s. This is referred to as pulse B. ResidualH₂O and reaction byproducts were removed by purging the reaction chamberfor 4.0 s. This is referred to as purge B. During each of the reactionphases, the reactants are supplied in sufficient quantity for the givenother parameters to saturate the surface.

This exemplary high-k deposition cycle is summarized in Table II. TABLEII ZrO₂ Temperature Pressure Time Phase Reactant (° C.) (mbar) (sec)pulse A ZrCl₄ 300 5-10 1.5 purge A — 300 5-10 3.0 pulse B H₂O 300 5-103.0 purge B — 300 5-10 4.0

The cycle of Table II, consisting of pulse A, purge A, pulse B, purge B,was repeated 51 times. The average deposition rate is about 0.59 Å/cycleat 300° C., such that the ZrO₂ thickness was about 30 Å.

More generally, temperatures during an ALD process preferably fallbetween about 200° C. and 500° C., depending upon the acceptable levelof chlorine incorporation into the layer. At higher temperatures, thechlorine content goes down. Too much chlorine can lead to chargetrapping. At 300° C. chlorine content has been measured at about 0.5%.For an amorphous ZrO₂ layer, the temperature is more preferably at thelow end of this range, between about 200° C. and 250° C., and mostpreferably at about 225° C. For a crystalline film, the temperature ismore preferably at the high end of this range, between about 250° C. and500° C., and most preferably about 300° C. As will be appreciated by theskilled artisan, however, mixtures of amorphous and crystallinecomposition result at the boundary of these two regimes. The illustratedprocess produces a largely crystalline ZrO₂ film.

In this case, the metal monolayer formed in the metal phase isself-terminated with chloride, which does not readily react with excessZrCl₄ under the preferred conditions. The preferred oxygen source gas,however, reacts with or adsorbs upon the chloride-terminated surfaceduring the oxygen phase in a ligand-exchange reaction limited by thesupply of zirconium chloride complexes previously adsorbed. Moreover,oxidation leaves a hydroxyl and oxygen bridge termination that does notfurther react with excess oxidant in the saturative phase.

Preferably, sufficient cycles are conducted to grow between about 20 Åand 60 Å of ZrO₂. More preferably, sufficient cycles are conducted togrow between about 20 Å and 40 Å. The dielectric constant of the layeris between about 18 and 24. In the illustrated examples, 30 Å of Zr₂O₃was formed.

An excited species treatment 125 follows dielectric formation 120.Whether the dielectric comprises conventional silicon oxide or a high kmaterial (having a dielectric constant or k value greater than about 4),the excited species treatment 125 advantageously facilitates polysiliconor poly-SiGe nucleation over the dielectric surface. The invention canalso have application to facilitating nucleation of SiGeC and siliconnitride or Al₂O₃ layers deposited over the high k material by CVD. Thedescribed treatment has also been found to have additional benefits inprotecting the high k material and underlying substrate from degradationduring subsequent processing, as will be described in more detail withrespect to FIGS. 4A and 4B below.

Like the excited species treatment 110 preceding ALD, the treatment 125preceding silicon or poly-SiGe deposition modifies the surfacetermination of the substrate to promote subsequent deposition.Advantageously, the treatment 125 is tuned such that the excited speciesimpart sufficient activation energy to break the surface bonds and formnew ones, while process parameters are tuned to maintain energy levelslow enough to prevent etching of the substrate or significant diffusionof active species into the bulk material of the gate dielectric.Additionally, no appreciable deposition takes place. At the most, amonolayer of terminating tails is left by the excited species treatment125. However, the process can be tuned to convert the topmost fewmonolayers of high k oxide to nitride by breaking metal-oxygen bonds andreplacing them with metal-nitrogen bonds. Preferably, temperatures arekept between about room temperature and 800° C.

The excited species treatment 125 can be conducted in the same chamberas the preceding dielectric deposition 120, but is more preferablyconducted in the same chamber as the subsequent electrode formation 130.Accordingly, temperatures during the treatment 125 are preferablymatched with at least the initial stages of polysilicon or poly-SiGedeposition conditions, while other parameters (pressure, reactantconcentration, plasma power, process duration) are optimized to have thedesired surface modification with minimal bulk effects. In theillustrated embodiments, wherein subsequent electrode formation 130comprises polysilicon or poly-SiGe deposition by CVD, temperaturesduring the treatment 125 are more preferably in the range of about 300°C. to 800° C., and most preferably from about 500° C. to 700° C.

In one embodiment, the excited species treatment 125 includes exposureto fluorine or chlorine radicals in sufficient supply to break surfacebonds, but insufficient to etch the preferred high k surface. Sourcesgases provided to the preferred remote plasma generator 60 (FIG. 2)include NF₃, F₂, B₂F₆, Cl₂, CF₄, etc. Argon, helium or other inert gascan also flow to aid formation of glow discharge, but reaction chamberpressure is preferably kept below about 10 Torr for maintainingoperation of the remote plasma unit.

Preferably, the process parameters are tuned to be sufficient forbreaking surface bonds without significant bulk modification. In thecase of in situ deposition 130 of the gate electrode, the substratetemperature is preferably set to match that desired for the subsequentdeposition within the same chamber. For the given temperature, pressure,remote plasma power, process duration and reactant concentrations can beadjusted to for the desired surface conditioning.

In another embodiment, a nitrogen source, such as ammonia (NH₃) ornitrogen gas (N₂) can be supplied to the substrate to break surfacebonds and create metal-nitrogen. N₂ is particularly preferred as thenitrogen source to minimize hydrogen content in the process. Argon,helium or other inert gas can also flow to aid formation of glowdischarge, but reaction chamber pressure is preferably kept below about10 Torr for maintaining operation of the remote plasma unit.

As noted, the process 125 does result in any significant deposition orincreased thickness. Process parameters are preferably selected toreplace metal-oxygen bonds in the upper few monolayers of the high kdielectric with metal-nitrogen bonds, forming a metal oxynitride. Inparticular, the excited species treatment 125 of the high k dielectricpreferably converts less than about 10 Å of the dielectric surface tosilicon oxynitride, more preferably forming about 2 Å to 5 Å on average.At the same time, energy levels in the process are maintained to avoidsignificant nitrogen diffusion into the bulk dielectric, beyond thenitrogen incorporation in the upper few monolayers of the dielectric.Preferably, the bulk dielectric contains less than about 10% atomicconcentration of nitrogen at a depth of 10 Å.

Next, the gate electrode is deposited 130 over the treated gatedielectric, preferably in the same chamber as the prior surfacetreatment 125 and preferably in situ doped. The gate electrodepreferably contains silicon and is CVD deposited. In the exampledescribed herein, the gate electrode comprises a CVD silicon germaniumalloy, preferably having the form Si_(1-x)Ge_(x), deposited by flowing asilicon source (SiH₄ in the illustrated example) and a germanium source(germane or GeH₄ in the illustrated example) over the treated gatedielectric. The prior remote plasma treatment 125, however, is also ofbenefit for other nucleation-sensitive deposition processes.

For simplicity, the silicon germanium layer will be referred to moregenerally as poly-SiGe. Preferably, the poly-SiGe deposition 130immediately follows excited species surface treatment 125 within thesame chamber. Alternatively, an initial silicon seed layer can bedeposited prior to poly-SiGe. Preferably, either polysilicon orpoly-SiGe deposition is conducted under atmospheric or near-atmosphericconditions.

As noted, the deposition of poly-SiGe preferably comprises flowing asilicon source gas, a germanium source gas and a carrier gas in achemical vapor deposition process. In the illustrated embodiment, thesilicon source gas comprises monosilane (SiH₄), the germanium source gascomprises dilute germane (1.5% GeH₄ in an inert gas), and the carriergas comprises nitrogen (N₂). The silane flow can be between 50 sccm and500 sccm, more preferably between about 100 sccm and 400 sccm. Thedilute germane (1.5% germane in the illustrated embodiment) ispreferably provided at a rate between 50 sccm and 5,000 sccm, morepreferably between about 100 sccm and 1,000 sccm. The carrier flow ispreferably between 5 slm and 50 slm, more preferably about 20 slm.

In the illustrated embodiment, without the aid of plasma or othersupplemental energy sources, temperature during the depositionpreferably is between about 500° C. and 800° C., more preferably betweenabout 550° C. and 650° C., most preferably is at about 600° C. plus orminus 15° C. At the lower end of these ranges, poly-SiGe deposition istoo slow for commercial applications. At the upper end of these ranges,on the other hand, germanium incorporation into the layer is reduced andsurface roughness increases. For alternative silicon source gases, suchas disilane and trisilane, the temperature for the deposition can be aslow as 300° C., at least initially, with a preferred range of 500° C. to700° C. Advantageously, such higher order silanes exhibit a lowerhydrogen:silicon ratio, and thus reduces risk of hydrogen diffusionthrough the surface and consequent reduction of the high k material tometal.

The poly-SiGe deposition is preferably conducted at greater than about500 Torr, more preferably at greater than about 700 Torr, and is mostpreferably conducted at about atmospheric pressure (760 Torr). Slightpressure differentials due to gas flows are of negligible effect. Aswill be appreciated by the skilled artisan, atmospheric depositionreduces the efficiency with which precursors are converted to depositedpoly-SiGe. However, the inventor has found deposition under atmosphericpressures to attain greater benefits to operational efficiency.

The germanium content in the poly-SiGe layer is preferably between about10% and 80%, more preferably between about 20% and 50%. The overallthickness of the layer is preferably between 500 Å and 1,500 Å, and morepreferably between about 500 Å and 1,000 Å.

An exemplary recipe for poly-SiGe deposition, using H₂ carrier gas,includes flow of about 500 sccm 1.5% germane, 100 sccm silane and 20 simcarrier gas at atmospheric pressure and 600° C. The skilled artisan willappreciate that the conditions should be separately optimized forperformance with an N₂ carrier gas. Such flows produce a silicongermanium layer with a germanium content of between about 18% and 20%.With the same carrier and silane flow, 4,500 sccm dilute germane silaneproduces a germanium content of about 50%.

Poly-SiGe deposition 130 is most preferably followed by deposition of acap layer. The cap layer preferably comprises silicon, and mostpreferably amorphous silicon. A relatively thin cap layer (e.g., about100 Å) can be employed to minimize the risk of oxidizing germanium inthe SiGe layer. On the other hand, the cap layer may also serve as asacrificial layer for later silicidation, in accordance with many gatestack designs. In this case, the cap layer is thicker and is preferablybetween about 1,000 Å and 2,500 Å. The amorphous silicon cap can befollowed by formation of a metal layer over the cap layer. This metallayer can then be annealed to react the overlying metal with theunderlying silicon, in a standard silicidation reaction. While notillustrated, a dielectric cap layer can also be deposited over theconductive layers of the gate stack described above.

Once the gate stack has been completed, the gate electrodes arepreferably patterned by conventional photolithographic techniques andetching. In other arrangements, the gate electrodes can be patternedprior to deposition of the metal layer, and the metal can be employed ina self-aligned silicidation, as is known in the art.

Having completed the gate stack, further processing to complete theintegrated circuit follows. For example, gate stacks typically areinsulated by blanket deposition of a dielectric and spacer etch.Transistor active areas are then doped to form source and drain regionsto either side of the patterned electrodes, and wiring or “back end”processes complete the circuit.

Advantageously, the excited species treatments 110 (prior to ALD) and125 (prior to poly-SiGe deposition) facilitates deposition over thetreated surface. In the first example, the excited species treatment 110facilitates adsorption of ALD reactants, and it will be appreciated thatsuch benefit will attach in various other contexts where ALD is desiredover a non-reactive substrate.

In the second example, surface treatment 125 enables rapid incubationand therefore faster deposition times for the overlyingsilicon-containing layer, such as the illustrated poly-SiGe layer, aswell as better overall layer quality. Direct deposition of in situgermanium-doped silicon layers (without excited species treatment 125)tends to etch the underlying gate dielectric in competition withdeposition, thus increasing incubation times. As will be appreciated bythe skilled artisan, the increased incubation time and consequentincrease in overall deposition time results in lower wafer throughput,which can mean the difference between commercially viable and non-viableprocesses in the highly competitive semiconductor fabrication industry.Furthermore, better incubation also entails a higher quality layer. Theskilled artisan will appreciate, in view of the present disclosure, thatundoped silicon or polysilicon in situ doped with phosphorus, arsenic orboron will also experienced improved incubation times.

Remote plasma nitridation of a high k dielectric top surface, prior togate electrode formation, has been found to have additional benefits. Inaddition to improved nucleation of silicon-containing layers depositedthereover, the surface treatment has been found to also reducedegradation of the high k material during the subsequent deposition. Thethin nitride or oxynitride formed by the excited species treatment isbelieved to inhibit reduction of the high k material. Such reduction,which would leave conductive metal in place of metal oxide, canotherwise result from the gate electrode deposition, particularly wherethe deposition recipe employs a high hydrogen content and/or hightemperatures. Furthermore, oxygen diffusion through the high k layer canalso be inhibited by the minimal nitridization effected by the preferredexcited species treatments 110, 125.

FIGS. 4A and 4B illustrate a transistor gate incorporating such adielectric stack. In particular, a semiconductor substrate 200 is shownwith a transistor gate stack 210 formed thereover. In the illustratedembodiment, the substrate 200 comprises an upper portion of asingle-crystal silicon wafer, though the skilled artisan will appreciatethat the substrate can also comprise other semiconductor materials.

The gate stack 210 includes a poly-SiGe electrode layer 220, withsidewall spacers 230 and an insulating layer 240 protecting andisolating the electrode 220 in a conventional manner. Also illustratedis a more highly conductive strapping layer 250, typically includingmetal, over the poly-SiGe 220. The strap 250 facilitates rapid signalpropagation among transistor gates across the wafer, connecting thegates to logic circuits. In other arrangements, the gate electrode maycomprise an in situ doped polysilicon layer.

A gate dielectric 260, formed by the exemplary processes describedabove, separates the gate electrode 220 from the substrate 200. As notedin the Background section above, the gate dielectric 260 is a criticalfeature in the pursuit of denser and faster circuits.

As best seen from the enlarged view of FIG. 4B, the preferred gatedielectric 260 includes an interface 262 with the underlying substrate200, a bulk dielectric layer 264, and an interface 266 with theoverlying gate electrode 220. The interfaces 262, 266 of the illustratedembodiment do not represent deposited layers; rather, the interfaceshave been slightly modified prior to the deposition of the layerthereover. In other arrangements, the plasma treatments could leaveadditional layers. In the illustrated embodiments, a remote plasmaprovides radicals for modifying the first interface 262 immediatelyprior to ALD, where the surface modification facilitates adsorption ofALD reactants. A remote plasma also provide radicals for modifying thesecond interface 266 immediately prior to in situ deposition ofsilicon-containing layers, such as polysilicon, and particularlyintrinsic polysilicon and poly-SiGe deposition by CVD, where the surfacemodification facilitates nucleation of poly-SiGe. In the case of remoteplasma nitridation, the lower interface 262 comprises a nitridizedportion of the substrate 200 preferably extending less than about 10 Åinto the substrate 200, more preferably comprising about 3 Å to 5 Å.Preferably the bulk substrate underneath this interface 262 containsless than about 1 atomic % nitrogen. The upper interface 266 similarlypreferably exhibits a low percentage of nitrogen (preferably less than10 atomic %) at a distance of 10 Å below the gate electrode 220.

In one embodiment, a transistor gate stack is formed by first forming agate dielectric over a semiconductor substrate. The gate dielectric isthen exposed to a source of nitrogen excited species. This exposurecauses less than about 10 atomic % nitrogen at a depth of greater thanabout 10 Å from an upper surface of the gate dielectric to beincorporated into the gate dielectric. A silicon-containing gateelectrode is then deposited over the gate dielectric.

It will be appreciated by those skilled in the art that variousomissions, additions and modifications may be made to the processesdescribed above without departing from the scope of the invention, andall such modifications and changes are intended to fall within the scopeof the invention, as defined by the appended claims. For example, whileillustrated in the context of surface treatment prior to ALD and CVD,the skilled artisan may also find application for radical treatment ofsurfaces prior to other forms of deposition, including but not limitedto MOCVD and JVD.

1. A method comprising: forming a layer of dielectric material over asubstrate; exposing the layer of dielectric material to a source ofnitrogen excited species, wherein exposing incorporates less than about10 atomic percent nitrogen at a depth of greater than about 10 Å from anupper surface of the layer of dielectric material; and depositing aconductor over the layer of dielectric material after exposing the layerof dielectric material to the source of nitrogen excited species,wherein the conductor contacts a portion of the layer of dielectricmaterial exposed to the source of nitrogen excited species.
 2. Themethod of claim 1, wherein the substrate is electrically conductive. 3.The method of claim 1, wherein the layer of dielectric material is atransistor gate dielectric layer.
 4. The method of claim 1, wherein thelayer of dielectric material has a dielectric constant of greater thanabout
 4. 5. The method of claim 1, wherein exposing incorporates lessthan about 1 atomic percent nitrogen at a depth of greater than about 10Å from the surface.
 6. The method of claim 1, wherein the layer ofdielectric material comprises a material selected from the groupconsisting of aluminum oxide, zirconium oxide, hafnium oxide, tantalumoxide, barium strontium titanate and strontium bismuth tantalate.
 7. Themethod of claim 6, wherein the layer of dielectric material compriseszirconium oxide.
 8. The method of claim 1, wherein forming the layer ofdielectric material comprises an atomic layer deposition.
 9. The methodof claim 1, wherein depositing the conductor comprises a chemical vapordeposition.
 10. A method of treating a surface of a dielectric materialin a partially fabricated integrated circuit, the method comprising:exposing the surface to products of a plasma, thereby modifyingtermination of the surface without significantly affecting bulkproperties beneath the surface, and without depositing a layer greaterthan about one atomic monolayer; and depositing an electricallyconductive layer thereover after modifying the surface termination. 11.The method of claim 10, wherein the dielectric material forms part of acapacitor.
 12. The method of claim 10, wherein the dielectric materialforms part of a transistor.
 13. The method of claim 10, wherein thedielectric material is a high-k dielectric material.
 14. The method ofclaim 10, wherein exposing comprises providing a flow of radicals from aremote plasma source to the surface.
 15. The method of claim 14, whereinthe flow of radical is stopped before depositing.
 16. The method ofclaim 10, wherein: the products of the plasma comprise nitrogen excitedspecies; the dielectric material has a dielectric constant greater thanabout 4; and the dielectric material comprises less than about 10 atomicpercent nitrogen at about 10 Å from the surface.
 17. The method of claim16, wherein the dielectric material comprises less than about 1 atomicpercent nitrogen at about 10 Å from the surface.
 18. The method of claim10, wherein the dielectric material is positioned between twoelectrically conductive layers.
 19. The method of claim 10, wherein theplasma is generated remote from the surface.